1. Field of the Invention
The present invention relates to a method and an apparatus for the acquisition of data for determining the duration and frequency modulation ("chirp") of a single ultrashort pulse in the optical spectral range as can be generated for example with a distributed feedback dye laser or a phase-locked dye laser with simultaneous use of frequency-changing and intensifying components and dispersing optical elements.
2. Description of the Related Art
The determination of the frequency modulation ("chirp") of ultrashort pulses, in particular of pulses having a duration in the picosecond (ps) and femtosecond (fs) range, was hitherto possible only with the aid of the socalled interferometric autocorrelation method of the second order, both by the multiple pulse process (Diels, Fontaine, McMichael and Simoni, Appl. Opt. 24, 1270 (1985)), and by the single pulse process (Szabo, Bor and Muller, Opt. Lett. 13, 746 (1988)). However, these methods permit only the determination of chirps of pulses with values of .alpha..gtoreq.3 . . . 4 (cf. equation 15a) below).
From the publication by Treacy, IEEE J. Quant. Electron. QE-5, 454 (1969), an apparatus generally referred to as TREACY compressor is known for compression (shortening) optical radiation pulses, the mode of operation of which can be described by the following relationship: ##EQU1##
Herein, .mu. is the parameter defining the group delay dispersion, l the perpendicular centre distance between the two diffraction gratings (the double passage employed here through the TREACY compressor is taken into account by the factor 2: l'=2.l), d is the grating constant, c the velocity of light, .omega..sub.0 the carrier frequency of the optical pulse and .gamma. the angle of incidence, measured between the incident ray and the grating normal.